1. Field of the Invention
The present invention relates to an apparatus and a method for measuring an altitude of a terminal More particularly, the present invention relates to an apparatus and a method for measuring an altitude of a terminal which can correct an altitude error according to temporal and spatial changes.
2. Description of the Related Art
Currently, a terminal, such as a smart phone, may be equipped with many different applications and functions including a barometer. Using the barometer, a value of atmospheric pressure at a user's current position may be measured.
FIG. 1 is a diagram for describing a driving principle of a barometer according to the related art.
Referring to FIG. 1, based on the driving principle of the barometer, a crystal within the barometer checks a vibration due to the atmospheric pressure and transmits the vibration as a signal to measure the atmospheric pressure. To check the vibration, each crystal is included within a cell. In general, a barometer uses an average of three cells to obtain a reliable value of atmospheric pressure without causing the cost of the device to become too high. That is, the price becomes more expensive as the number of cells increases.
Also, while the terminal may measure the atmospheric pressure using the barometer, the barometer is generally only used for measuring an altitude.
As an alternative to using a barometer, a Global Positioning System (GPS) may be used because the GPS information includes altitude information as well as longitude/latitude information. However, the altitude information has large error ranges from several meters to dozens of meters. Therefore, the GPS is not suitable for precisely measuring an altitude.
Furthermore, since the GPS cannot be used indoors, it is not possible to use a service such as Indoor Navigation.
FIG. 2 is a graph illustrating a relation between an atmospheric pressure and an altitude according to the related art.
A reason why an altitude can be calculated through a barometer as illustrated in FIG. 2 is that there is a constant relation between the atmospheric pressure and the altitude. On earth, as an altitude becomes higher, the atmospheric pressure becomes lower. Since pressure is based on weight, as an altitude becomes higher, air becomes insufficient and thus the weight of air becomes lighter.
The relation between the atmospheric pressure and the altitude may be described through equation (1) below.
However, in order to calculate an altitude value according to the corresponding atmospheric pressure through Equation (1) below, a reference atmospheric pressure, such as the atmospheric pressure in a particular altitude, is required. Accordingly, a site, such as a weather center, provides an atmospheric pressure value at sea level (altitude 0 m).
                    ρ        =                                            ρ              b                        ·            exp                    ⁢                      ⌊                                                            -                                                            g                      0                                        .                    M                                                  ·                                  (                                      h                    -                                          h                      b                                                        )                                                                              R                  *                                ·                                  T                  b                                                      ⌋                                              (        1        )                            ρ: atmospheric pressure (kg/m3)        ρb: reference atmospheric pressure        h: altitude (geopotential meters)        hb: reference altitude (0 m)        Tb: standard temperature constant (k)        R*: Universal gas constant for air: 8.31432 N·m/(mol·K)        g0: acceleration of gravity (9.80665 m/s2)        M: Molar mass of Earth's air (0.0289644 kg/mol)        
As defined in Equation (1), in order to acquire the altitude through the atmospheric pressure measured by the barometer, the reference atmospheric pressure is required. In general, the reference atmospheric pressure is 1013.25 mbar (760 mmHg) at sea level (i.e., 0 m). Based on the reference atmospheric pressure, an altitude h may be calculated when an atmospheric pressure is p. However, such a method provides an accurate value only when the atmospheric pressure at sea level in a measured area corresponds to the reference atmospheric pressure. However, the atmospheric pressure at sea level may be different according to weather conditions time of day, and the season of the year.
Accordingly, in order to calculate an accurate altitude of a current position, external information, such as reference atmospheric pressure information, is required. However, there is a realistic limitation in the ability to collect the latest information all the time. Particularly, when the atmospheric pressure at sea level of the current position is acquired from the weather center, there are at least two risk factors as listed below.
1. Temporal Risk Factor
The first factor is time. Receiving the atmospheric pressure at sea level of the current position every minute or every second may be the best method. However, since the weather center mainly measures the atmospheric pressure at sea level every thirty minutes or every hour, it is realistically difficult to use the best method.
Actually, thirty minutes and one hour correspond to a long time in a viewpoint of atmospheric pressure. During one day, there is a difference in the atmospheric pressure according to morning, afternoon, and evening, and there is deviation for each season. Accordingly, an error is actually generated during such a time. Therefore, a technology for correcting the reference atmospheric pressure by considering the error even though time goes by is required.
2. Spatial Risk Factor
The second factor is space. Strictly speaking, the atmospheric pressure at sea level refers to the atmospheric pressure at sea level at the weather station. Accordingly, there is no problem when a distance between the weather station and the terminal is short. However, reliability of reference atmospheric pressure information decreases when the distance is long.
Further, land movement, ranging from dozens of kilometers to hundreds of kilometers per hour, are currently possible due to the development of land transportation. However, when movement to a particular area is made before the reference atmospheric pressure is updated, an error is generated because the reference atmospheric pressure of a previous area is used as the reference.
Therefore, a need exists for an apparatus and a method for measuring an altitude of a terminal which can correct an altitude error by extracting a reference atmospheric pressure corresponding to a spatial change and using the extracted reference atmospheric pressure.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.